In this image taken from amateur video smokes rises from an accidental explosion at a Revolutionary Guard ammunition depot outside Bidganeh village,west of Tehran which killed at least 15 people on Saturday, officials said. The explosions occurred at a base located outside Bidganeh village, 25 miles southwest of the capital.

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Istanbul, Turkey

Mystery surrounds yesterday's explosion at a Revolutionary Guard ammunition depot that was so large it was felt and heard almost 30 miles away in Tehran.

Even as funerals began on Sunday for the 15 soldiers killed, Iranian commanders sought to downplay any connection to Iran's advanced ballistic missile arsenal and its controversial nuclear program.

The explosion comes as Iran is locked in a tense standoff with the US, Israel, and the West over its nuclear program, which last week produced a surge of threats and counter-threats of military action over the release of a United Nations report that detailed what it called "credible" evidence of Iran's past work on nuclear weapons technologies.

The Fars News Agency, which is connected to the Islamic Revolutionary Guard Corps (IRGC), reported on Sunday that the IRGC "strongly dismissed certain baseless reports" that the explosion was "related to nuclear tests or transport of missile warheads."

"The blast happened during the transportation of [conventional] ammunition," said the IRGC press chief General Ramazan Sharif. Some 15 soldiers had been "martyred," he said, dialing down initial estimates of 40, though some of the wounded were in critical condition.

Iranian media reports said the blast took place at an ammunition depot at an IRGC base in the village of Bidganeh, near Malard in the Northern Alborz province, some 30 miles west of Tehran. Officials ruled out sabotage.

Residents of the Iranian capital and the city of Karaj, respectively 30 miles west and seven miles north of the blast area, felt its power.

"Our windows shook," said a Karaj resident, who says she and her neighbors believed it to be thunder or an earthquake, according to a Financial Times in a report from Tehran.

"I heard in my yoga class today that it was a missile attack but we do not know if it was by the US or Israel," said another Karaj resident, called Farshid.

Israeli Prime Minister Benjamin Netanyahu sought last week to convince his cabinet to back military strikes against Iranian nuclear facilities, saying that a nuclear-armed Iran would be an "existential threat" to the Jewish State.

Successive US presidents have also declared that a nuclear Iran would be "unacceptable," and left "all options" – including military action – on the table.

The Nov. 8 report by the UN International Atomic Energy Agency (IAEA) stated that "systematic" weapons-related work was halted in 2003, though some aspects "may" continue. It confirmed that no declared nuclear material had been diverted from civilian use.

Iran denies seeking nuclear weapons. But US lawmakers said the report amounted to a "smoking gun" and called for "crippling sanctions" against the Islamic Republic.

GOP candidates sound hawkish note

Republic presidential candidates went much further at a debate on Saturday night in South Carolina, as they tried to outdo each other with anti-Iran rhetoric.

Former Sen. Rick Santorum (R) of Pennsylvania said the US should work closely with Israel to strike Iran's nuclear facilities – as it took out Iraq's in 1981 and Syria's in 2007 – "before the next explosion we hear in Iran is a nuclear one and then the world changes."

Iran's supreme religious leader Ayatollah Ali Khamenei vowed on Thursday that any attack against Iran would be met with a "strong slap and iron fists."

As Israel test-fired an intercontinental ballistic missile a week ago – the first such test since 2008 of the Jericho III, which has a range at least three times that of any target in Iran – Iranian lawmakers made clear the result if Iran were targeted.

That battle would extend "with maximum might and power all throughout the European and US soil, if Iran comes under attack," Seyed Hossein Naqavi, a member of parliament's security commission, told Fars News.

Speculation surrounding Iran opposition group's claims

Speculation about the reasons behind the Saturday blast was fueled by claims from an Iranian opposition group that it occurred at an IRGC missile base, and not a conventional weapons depot.

The Mojahedin-e Khalq (the MEK aka MKO) claimed that the blast at the Modarres Garrison "resulted from the explosion of IRGC missiles," according to an e-mail communication with the Associated Press from Alireza Jafarzadeh, an MEK spokesman in Washington until it the group was put on the US State Department's terrorism list.

Mr. Jafarzadeh in 2002 announced the existence of undeclared Iranian uranium enrichment facility at Natanz, using data widely believed to have come from Israel. Since the MEK was put on the US State Department's terrorist list, Jafarzadeh has been an "Iran analyst" on Fox News and lobbied in Washington to have the MEK taken off the terror list.

UN weapons inspectors say much of the data passed to it by the MEK over the last decade has proven inaccurate.

A detailed 150-page dossier on Iran's ballistic missile capabilities produced in May 2010 by the International Institute for Strategic Studies in London makes no mention of any missile-related facility at Bidganeh or Malard, nor of the "Modarres Garrison."

It does, however, describe a Sajjid Base near Karaj – north of the location of Saturday's explosion – where Iran's 19th Zolfaqar Missile Brigade reportedly deploys 125-mile range Zelzal "Earthquake" rockets. The source cited for that 2002 information, however, was the MEK.